After creating any of these services, you will be able to view your custom MX record in the DuoCircle control panel. After sign-in, click on the "My Services" link then click the table row for the relevant service, in your enterprise email servers plan. On that page look for "Your Custom MX" under the Service Settings heading and use the value provided to its right. This custom MX record will be of the format a######.mx.mailhop.org or the record specified in your account.

This must be set accordingly with your domain registrar or DNS provider for the service to work correctly.

This can be done by logging into your domain registrar or DNS provider's control panel and locating your current MX records for the relevant domain.